Shape memory alloys are known and are usually made predominantly or wholly of titanium and nickel. They may also include other material, such as aluminium, zinc and copper. A shape memory alloy is capable of adopting one shape below a predetermined transition temperature (Martensitic) and changing to a second shape once its temperature exceeds the transition temperature (Austenitic). Conversely, when the shape memory alloy cools below the transition temperature, it is capable of adopting the first shape again. In connection with the various aspects of the present invention, the shape memory alloy contracts when heated in situ. Shape memory alloy wire currently available, such as that sold under the name Nitinol, is capable of contracting by about 3% when activated by heating.
Activation of shape memory alloy (SMA) such as Nitinol is preferably achieved through electrical resistance heating.
Shape memory alloy wire is known to exhibit a number of behavioural characteristics which may affect performance and life of the wire.